Israeli Prime Minister Ariel Sharon has undergone nearly four hours of "successful" surgery in Jerusalem after a deterioration in his health.
Doctors removed one third of Mr Sharon's large intestine after finding damage to his digestive tract.
Later the hospital director declared: "There is no immediate danger to [Mr Sharon's] health."
Mr Sharon, 77, has been in a coma since 4 January, when he suffered a severe stroke and underwent surgery.
Interim Prime Minister Ehud Olmert assumed his powers in January.
'Critical but stable'
Shortly after the operation, Hadassah hospital spokesman Ron Krumer declared the operation to be "a success".
ARIEL SHARON'S HEALTH
18 Dec 2005: Sharon suffers minor stroke
4 Jan 2006: Sharon rushed to hospital one day before scheduled heart surgery with major stroke
4/5 Jan: Undergoes two operations overnight
6 Jan: Third round of surgery
9 Jan: Doctors start to try to rouse him from medically induced coma
15 Jan: Has tracheotomy to help to wean him off respirator
25 Jan: Medical team hold talks with long-term care specialists
1 Feb: Doctors insert feeding tube into stomach
10 Feb: Brain scan shows no change in condition
11 Feb: Has emergency surgery after condition worsens
Mr Sharon is now back in intensive care.
Later the director of the Hadassah hospital, Shlomo Mor-Yosef, told journalists that Mr Sharon's condition was "critical but stable. There is no immediate danger to his life".
Dr Mor-Yosef said the decision to operate was taken after consultations with Mr Sharon's two sons.
An initial laparoscopy showed that Mr Sharon's condition "seemed to be life-threatening".
The large intestine was "damaged, inflamed, infected". Surgeons removed "about 50 cm (20 inches) of the large intestine".
However, Dr Mor-Yosef stressed that Mr Sharon's most serious concern was not his abdominal complications but the coma.
"The main problem is him still being unconscious. There is no significant change in that."
Relatives and staff began arriving at the hospital soon after news of the decline in his health emerged.
Doctors carried out the abdominal scan on Saturday morning and then moved him into surgery at about 1100 (0900 GMT).
Mr Sharon is in a frail condition after several operations following his stroke.
His failure to wake up after being taken off sedatives last month has led to speculation that he has suffered severe brain damage.
His deputy Ehud Olmert will lead the newly formed centrist Kadima party in the general election on 28 March.
Mr Olmert has been Mr Sharon's closest political ally for most of the past decade and is seen as the politician most likely to continue his legacy.
He has said that if he wins next month's poll, Israel will retain West Bank settlement blocs and Jerusalem.
However, he also said that Israel would be prepared to give up parts of the West Bank where most Palestinians were living.
Israeli leaders say they will not deal with a Palestinian government including Hamas, following the Islamic militant group's sweeping victory in polls last month.
Israel regards Hamas as a terrorist group committed to the destruction of the Jewish state.
The political leader of Hamas says the group is ready to talk to Israel, but will not renounce violence.